SYNERGISTIC ACTIONS OF INTRAVENOUS ANESTHETICS

描述(申请人提供)：γ-氨基丁酸A型(GaBAA)受体是递质门控离子通道Cys-loop家族的成员。受体对突触释放的或周围的递质做出构象变化的反应，导致门的打开，允许离子通过通道移动。增强GABAA受体活性是许多静脉麻醉药的麻醉效果的基础，如依托咪酯和异丙酚。尽管在临床上并不活跃，但神经活性类固醇是最有效的GABAA受体增强剂之一。异丙酚、依托咪酯和神经活性类固醇也直接激活GABAA受体，尽管直接激活的浓度通常高于引起增强的浓度。我们的初步数据显示，一些神经活性类固醇强烈加强异丙酚或依托咪酯的门控作用。低浓度的GABA和低浓度的类固醇的组合导致显著的、超添加剂的增强程度的增加。在蝌蚪和小鼠的行为测试中，存在低的亚阈值浓度的增强型类固醇会导致翻正丧失的剂量-反应关系左移，而在细胞系中，类固醇的存在不会影响依托咪酯对皮质醇释放的抑制。本工作的总体目标是确定类固醇类似物和静脉麻醉剂对GABAA受体的作用机制，并探讨该发现的临床意义。我们将：i)检测类固醇和别类固醇激动剂对异源表达系统中表达的重组突触和突触外GABA的协同效应；ii)在蝌蚪和小鼠的行为检测中检测类固醇和静脉麻醉剂协同作用的行为后果；以及iii)探索在类固醇存在的情况下产生镇静所需的麻醉药剂量减少是否导致非靶点效应的减少。这些目标的完成将增加我们对GABAA受体在健康和疾病中的作用的了解，并为未来开发新的治疗方法奠定基础。

DESCRIPTION (provided by applicant): The γ-aminobutyric acid type A (GABAA) receptor is a member of the Cys-loop family of transmitter-gated ion channels. The receptors respond to synaptically-released or ambient transmitter with a conformational change, resulting in the opening of the gate that allows ion movement through the channel. Potentiation of GABAA receptor activity underlies the anesthetic effects of many intravenous anesthetics, such as etomidate and propofol. Although not in active clinical use, neuroactive steroids are among the most potent and efficacious potentiators of the GABAA receptor. Propofol, etomidate and neuroactive steroids also directly activate the GABAA receptor, although the concentrations for direct activation are typically higher than those that cause potentiation. Our preliminary data demonstrate that some neuroactive steroids strongly potentiate gating by propofol or etomidate. Combination of a low concentration of GABA with a low concentration of steroid results in a remarkable, supra-additive, increase in the extent of potentiation. In tadpole and mouse behavioral assays, the presence of a low, subthreshold concentration of a potentiating steroid results in a leftward shift in the dose-response relationship for loss of righting whereas in a cel line the presence of a steroid does not affect etomidate-elicited suppression of cortisol release. The overall goal of the present work is to determine the mechanism of interactions of steroid analogues and intravenous anesthetics on GABAA receptors, and to explore the clinical significance of the findings. We will: i) examine the synergistic effects of steroids with allosterc activators on recombinant synaptic and extrasynaptic GABA expressed in heterologous expression systems; ii) examine the behavioral consequences of synergistic effects of steroids and intravenous anesthetics in tadpole and mouse behavioral assays; and iii) probe whether reduced doses of anesthetics required to produce sedation in the presence of steroids lead to reduced off-target effects. The completion of these aims will increase our understanding of how the GABAA receptor functions in health and disease, and lay a foundation for future development of novel therapeutic approaches.